This invention relates to an improved heat transfer fin structure of the type normally fabricated from sheet metal and operable to be secured to an object to provide increased effective surface area to the object for enhanced transfer of heat between the object and a fluid in contact with the object.
The invention relates more particularly to an improved heat transfer fin structure which not only has high heat transfer efficiency but also has relatively high peripheral stability or resistance to physical deformations.
In particular, in order to appreciate fully the inventive advance of the present invention over the previous heat transfer fin design, consideration is to be given to a number of related heat transfer fin structures which are of interest. It is noted that a large number of patents describing configurations for fin strips to be applied to tubing carrying a heat exchange medium to increase the heat transfer between the medium within the tube and a circulating, generally gaseous medium, which circulates over the fins, have been granted. The systems proposed by the prior art include fins struck from the surface of the tubing, tubing formed by wrapping and welding of the fin surface, and a large number of configurations which involve wrapping of the tubing with a fin strip or coiled wire. In each case, improved heat transfer between the fluid circulating through the tubing and the generally gaseous materials circulating over the fin surface is obtained.
However, as is apparent from the number of patents which have issued in this area, an optimum structure remained to be found. The problem which plagued the prior art systems, and which the instant invention endeavors to overcome, is the practical problem that the various structures devised to increase surface area resulted in a decreased peripheral stability of the structure. Structures devised which had high peripheral stability normally traded heat exchange efficiency for the enhanced stability. This problem can be best illustrated by the short review of a number of patents which reflect the prior art structures, which follows below. Only a few of the large number of issued patents in this field have been chosen for discussions as being somewhat representative of the various structures previously employed.
The structures which provide high heat exchange efficiency are normally of the bristle fin type of construction. The U.S. Pat. Nos. 2,234,423 to Wittmann and 2,247,243 to Kritzer both show a similar bristle type of structure wherein spikes or legs are disposed extending generally outwardly from a conduit to which it is desired to give enhanced heat exchange efficiency. As is well known in the art, the higher the surface area that is effectively displayed by the conduit, the greater will be the efficiency of heat exchange between the conduit and a fluid in contact with the conduit. The Mcturk U.S. Pat. No. 2,453,448 shows another similar structure wherein wires form a bristle-like heat exchange structure.
It is easily seen that the above noted structures may be easily physically deformed.
A considerably more robust structure, but one which has greatly decreased heat exchange efficiency is disclosed in U.S. Pat. No. 2,529,545, to Edwards. Edwards shows a solid spiral or disc structure secured to a conduit. The solid structure has much higher peripheral stability then the bristle type structures discussed above, but, as is well known, it has much lower heat exchange efficiency.
A large number of structures which are intermediate the solid spiral structure and the bristle structures, have been devised. Examples of the structures are such as the radiator spiral coil tube of Emmons et al. U.S. Pat. No. 1,960,305. Emmons et al. teaches an open box like structure which is spiraled around a conduit. The Brown U.S. Pat. No. 2,355,621 uses a multiplicity of elongated solid fins. Rodeck U.S. Pat. No. 2,372,795 uses a solid spiral which has been cut and expanded into a multiplicity of relatively wide leg portions. The Brown, Jr. U.S. Pat. No. 2,400,737 shows a structure similar to the Rodeck structure.
The expanded metal type of structure shown in the patent to Poole U.S. Pat. No. 2,471,582, has the advantage over previously discussed structures in that there is an increased effective area and increased peripheral stability, however, as is well known, such a structure has reduced heat exchange efficiency when compared with a bristle type of fin structure.